Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$177.90	12.611%	$200.335	$200.34	$200.35	$200.30
Purchase #2	$164.56	12.787%	$185.6023	$185.60	$185.60	$185.60
Purchase #3	$80.30	11.697%	$89.6927	$89.69	$89.70	$89.70
Purchase #4	$95.70	8.145%	$103.4948	$103.49	$103.50	$103.50
Purchase #5	$79.78	10.501%	$88.1577	$88.16	$88.15	$88.20
Purchase #6	$69.81	9.791%	$76.6451	$76.65	$76.65	$76.60
Purchase #7	$230.68	5.792%	$244.041	$244.04	$244.05	$244.00
7 purchase totals =	$898.73		$987.9686	$987.97	$988.00	$987.90